(1) Field of the Invention
This invention relates to a polyolefin composition and the same that is especially suitable for use in producing vehicle exterior members. More particularly, the invention relates to a polyolefin composition which is excellent in several properties such as softness, impact resistance, shape restorable property, appearance of molded articles, moldability and paintability and which is useful in industrial fields, for example, the production of various exterior parts of automobiles.
(2) Description of the Prior Art
The thermoplastic polyolefin elastomer (TPE) has been hitherto used in various fields of industry because its specific gravity is low, thermal resistance is good and the balance among several properties, for example, between rigidity and impact resistance, is relatively good. In addition it is not expensive.
The TPE is generally a blended product of a hard segment of crystalline polypropylene (PP) or polyethylene and a soft segment of an olefin elastomer such as ethylenepropylene rubber (EPR), polyisobutylene or polybutadiene. It is often subjected to partial cross-linking treatment in order to improve its physical properties.
In recent years, however, especially with the expanding uses of the material for automobile parts, required properties have been diversified. For instance, with regard to automobile exterior members, required merits are good moldability, appearance (gloss) of molded articles, paintability, the property that the deformation caused by impact is easily restored (restorable property) as well as the thermal resistance and low-temperature impact resistance.
The conventional TPE could not always meet all of these requirements. For example, a composition of PP, EPR, polyethylene of 0.915-0.97 g/cm.sup.3 in density and peroxide is proposed in Japanese Laid-Open Patent Publication No. 54-41950; a composition of PP, EPR and medium density polyethylene is proposed in Japanese Laid-Open Patent Publication No. 55-139445; a composition of PP, EPR, high density polyethylene and talc is proposed in Japanese Patent Publication No. 59-49252 (U.S. Pat. No. 4,412,016); a composition of PP, EPR and ethylene-.alpha.-olefin linear copolymer is proposed in Japanese Laid-Open Patent Publication Nos. 58-42643 and 58-80335. Nevertheless, these compositions are still unsatisfactory in view of the balance between rigidity and low-temperature impact resistance. In addition, their restorable property is not good.